Projection screen



Dec. 18, 1934. o, VQN GRUBE 1,985,066

PROJECTION SCREEN Filed Dec. 21, 1933 9111111111 1111111111. I I I 1 1In venturi- Patented 18, 1934 PROJECTION SCREEN Otto von Gruber, Jena,Germany, assignor to ilrm Carl Zeiss, Jena, Germany Application December21,1933, Serial No. 703,445 In Germany December 24, 1932 2 Claims. (CI.33-40) The invention concerns a projection screen to ing to thedouble-projection method that the dibe used in apparatus for plottingmaps from rection of displacement X-X of the holder 1 is measuringimages projected on a screen surface. at right angles to the plane ofthe drawing. A When using screens of this kind, the necessity ring 3 ismounted on the holder 1 in such a manof an exact focusing of themeasuring mark in her as to be rotatable about an axis Y--Y, this thestereoscopic image produced by the projecring 3 supporting a projectionscreen 4 rotatable 5 tion of the measuring images of the object to beabout an axis 2-2. The point of intersection plotted requires asuillcient contrast between the of the said two-axes Y-Y and Z-Z lies inthe projection surface and the measuring mark. surface of the projectionscreen 4. This sur- The measuring marks generally applied so far face 5may be coated for instance with a layer have been black marks on asurface which reof white baryta. The projection screen 4 has a fleetsthe light diffusely. Use may be madeas triangular aperture 6 whose oneangle lies at the well of luminous marks, that is to say of markscardanic centre 0. This angle is used as ameasproduced by means of anaperture provided in uring mark in the scanning of the composite r theprojection screen and illuminated by a source stereoscopic image whichresults from the proof light disposed behind the screen. However,jection of two measuring images and corresponds 1 marks of this kind arenot very practical. to the object represented on the two measuringAccording to the invention, a measuring mark images by means of itssingle images. To the which comes up to all requirements is obtainedlower side of the projection screen 4 is attached by representing themark by means of an apera box 7 which is assumed to be lined forinstance ture in the projection screen and by providing with blackvelvet, this box 'I preventing the ac- 20 that this aperture appears asa black surface. cess of light to the lower side of the aperture 6 Thisis attained in the most simple manner by and absorbing the lightentering the aperture so dimensioning or constructing the projectionfrom above.

screen that the light rays for the projection of I claim:

the measuring images do not strike that side'oi' 1. A projection screenfor apparatus for plot- 25 the aperture which does not face theprojection ting maps from measuring images projected on chambers of theplotting apparatus. The most a screen surface, this projection screenhaving an convenient manner of avoiding this is to provide aperturewhich represents the measuring mark behind the aperture a closed chamberhaving of the apparatus, and means disposed behind this black interiorwalls. aperture and making the aperture appear black.

In the accompanying drawing, Figure 1 repre- 2. A projection screen forapparatus for plotsents an elevational section through, and Figure tingmaps from measuring images projected on 2 the top view of, a projectionscreen according a screen surface, this projection screen having to theinvention. an aperture which represents the measuring A semi-circularholder 1 is adjustably mountmark of the appar and a closed chamber 35edit: a guide 2 assumed to be so placed by means having black interiorwalls and being disposed of a foot on the drawing surface of aphotobehind the aperture. graphic plotting apparatus to be operatedaccord- O'IIO Von GRUBER.

